Touch sensor circuit

ABSTRACT

A touch sensor circuit includes a plurality of drive/receive circuits and a drive signal generation circuit. The drive/receive circuits drive and receive signals from a multi-touch sensor. A drive/receive circuit includes an analog to digital conversion (ADC) circuit and a digital to analog conversion (DAC) circuit. The ADC circuit includes a first input to receive a sensor signal on an electrode of the multi-touch sensor. The sensor signal includes a drive signal component and a receive signal component. The ADC circuit includes a second input to receive an analog reference signal from the drive signal generation circuit. The ADC circuit generates a digital signal based on the analog reference signal and the sensor signal. The DAC circuit converts the digital signal into the drive signal component and the receive signal component is representative of an impedance on the electrode detected and is indicative of a touch proximal to the electrode.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present U.S. Utility patent application claims priority pursuant to35 U.S.C. § 120 as a continuation of U.S. Utility application Ser. No.15/506,097, entitled “MULTI-TOUCH SENSOR AND ELECTROSTATIC PENDIGITIZING SYSTEM UTILIZING SIMULTANEOUS FUNCTIONS FOR IMPROVEDPERFORMANCE,” filed Feb. 23, 2017, pending, which is a U.S. NationalStage Application submitted pursuant to 35 U.S.C. § 371 of PatentCooperation Treaty Application No. PCT/US2016/038497, entitled“MULTI-TOUCH SENSOR AND ELECTROSTATIC PEN DIGITIZING SYSTEM UTILIZINGSIMULTANEOUS FUNCTIONS FOR IMPROVED PERFORMANCE,” filed Jun. 21, 2016,which claims priority pursuant to 35 U.S.C. § 119(e) to U.S. ProvisionalApplication No. 62/183,062, entitled “MULTI-TOUCH SENSOR ANDELECTROSTATIC PEN DIGITIZING SYSTEM UTILIZING SIMULTANEOUS FUNCTIONS FORIMPROVED PERFORMANCE,” filed Jun. 22, 2015, all of which are herebyincorporated herein by reference in their entirety and made part of thepresent U.S. Utility patent application for all purposes.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable.

INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC

Not Applicable.

BACKGROUND OF THE INVENTION Technical Field of the Invention

The invention relates in general to an improved multi-touch sensor andelectrostatic pen digitizing systems, circuits, and methods.

Description of Related Art

Projected capacitive touch sensors typically include a substrate uponwhich electrodes for sensing a touch location are disposed. Thesubstrate may be a durable glass having high optical transparency forviewing images displayed by an underlying display device that displaysimages such as graphical buttons and icons. When a user touches, forexample with a finger or a stylus, on the outer surface of the substrateat a location corresponding to a desired selection displayed on thedisplay device, the location is determined by sensing changes incapacitances to and between the electrodes.

In some projected capacitive touch sensors, the electrodes are arrangedin rows of electrodes and columns of electrodes. The rows and columnsare electrically isolated from one another via an insulating layer. Atouch location is determined by driving electrodes of a firstorientation (e.g., the column electrodes or drive electrodes) with asquare wave signal (i.e., drive pulse). Sense circuitry coupled to theelectrodes of the other orientation (e.g., the horizontal electrodes orsense electrodes) measures current flow between the electrodes due tomutual capacitive coupling that exists between the column electrodes andthe row electrodes. The amount of current flow is directly proportionalto the value of the mutual capacitance and therefore facilitates thedetermination of the mutual capacitance. The mutual capacitance betweenthe intersection of a column electrode and a row electrode will changewhen a user touches the substrate in the vicinity of the intersection.

Typically, sense circuits for measuring the mutual capacitance operateby repetitively switching the sense electrodes to an input of an analogintegrator circuit, which includes an amplifier with a feedback circuitthat includes a capacitor that couples the amplifier output to theamplifier input. Such a circuit typically comprises a switch thatcouples the input of the integrator to the sense electrode just beforeeach falling edge of the drive pulse that drives the drive electrodesand then uncouples just before each rising edge so as to integrate onlysignals of one polarity. The output of the integrator is then digitizedand the digitized value is utilized to determine whether and where atouch has occurred.

However, the relative magnitudes of parasitic capacitances of the switchat the input of the integrator are large in comparison with the mutualcapacitances between electrodes, which is typically measured infractions of a pico-farad. To overcome the effects caused by theparasitic capacitances, a number of integration cycles are performedbefore a touch location may accurately be determined. For example, theintegrator may integrate the signal measured on the sense electrode overtwo hundred or more cycles, which could take 1 ms or more for a drivepulse with a frequency of 200 kHz. The length of time to make adetermination increases with the number of electrodes that must bemeasured, which may affect user experience for relatively large displaysthat typically have a large number of electrodes to measure, relative tosmaller Cap displays used in mobile devices.

A touch location can also be determined by driving electrodes of a firstorientation only (e.g., the column electrodes) and sensing the currentchange only to the driven electrode. The sense circuitry measurescurrent flow changes to the electrodes due to electrodes self-capacitivecoupling that exists between the driven electrode and impedance paths toground which can include paths from the electrode to other electrodes.The amount of current flow is directly proportional to the value of theimpedance paths and therefore facilitates the determination of theself-capacitance. The self-capacitance will change when a user touchesthe substrate in the vicinity of the electrode altering the impedancepaths to other electrodes but also adding new paths through the user toany ground potential.

In typical multi-touch systems, the self-capacitive signal-to-noiseratio is much larger than the mutual capacitances due to the fact thatthat the self-capacitive signal contains the drive signal, the sensorparasitic capacitances, as well as the touch signal energy changewhereas the mutual capacitance signal is much smaller as it onlycontains the cross parasitic capacitance and touch signal energy change.Also in typical systems, the self-parasitic capacitances is largebecause the surrounding channels are effectively grounded as only onesignal is driven at a time. Surrounding channels in this case are thechannels adjacent and also crossing channels on a two-axis systemincluding the delivery traces to the touch area which are typically avery large portion of this parasitic capacitance. These parasiticcapacitances interact with the pulse or square wave driving and samplingwhich contain high frequency harmonics. These harmonics contain asignificant portion of the touch energy change which attenuates fasterthan the fundamental when passing down a RC impedance chain and backcausing considerable signal and increasing signal loss as thetouchscreen impedance rise.

In some previous capacitance touch sensor systems, the self-capacitancemeasurement has been used with guard electrodes where the adjacentelectrodes are driven with the same signals so as to shield theelectrode of interest from the current flow of the impedance paths ofthe target electrode and adjacent electrodes. The shielding also blockscurrent flow to further adjacent paths as the voltages of the adjacentshield electrodes supply almost all of the current and charging of thesefurther capacitances and impedance paths. When correctly executed thisself-capacitance measurement and shielding can be used to reduce theerror signal due to contamination by a conductor such as salt water,which will tend to add to the users touch and will tend to bridge energyto surrounding impedance paths. This adjacent shield method does notblock the alternate axis channels near and crossing the driven trace andso only shields about half the possible impedance paths. The ability tomeasure a touch in the presence of salt water contamination on the touchsensor is in some cases such as industrial, marine, or militaryapplications, highly desired but does not work well on the currentsolutions available.

Typical touch control circuits have the ability to measure the differentmodes self or mutual capacitance or even to measure only the un-drivenstate of the electrodes as a method of receiving only external signals.But aside from driving a few shield electrodes or a drive/sense pairtypically the modes of sampling can occur only one mode at a time. Thelength of time to make a determination for each mode increases with thenumber of electrodes that must be measured, which may affect userexperience for relatively large displays that typically have a largenumber of electrodes to measure, relative to smaller Cap displays usedin mobile devices.

Sigma-Delta Analog to Digital Converters (ADC) have been known for sometime but have recently become very popular as programmable logic clockspeeds have improved to the point where very good conversion function ispossible. Many new ideas and work centered on improving these convertersspeed and functionality has been in an effort to allow this more digitalconversion method to replace the more standard analog techniques. In thetouch realm, many improvement patents have been granted aroundincorporation of known capacitive sampling techniques and Delta Sigmaconversion of analog to digital.

U.S. Pat. No. 8,089,289 has an example of prior art technology using aDelta Sigma Converter and showing mutual capacitive scheme using squarewave drive and switched capacitor function with rectification in twoembodiment drawings of the same function, as shown in FIG. 20.

U.S. Pat. No. 7,528,755 shows an example of prior art technology using aDelta Sigma Converter and showing scheme capable of signal drive ormeasure technique selectable via a mux as shown in FIG. 21.

U.S. Pat. No. 8,547,114 shows an example of prior art technology using aDelta Sigma Converter and switched capacitor techniques as shown in FIG.22.

U.S. Pat. No. 8,587,535 shows an example of a prior art strategy, thisstate of the art mutual capacitance multi-touch system with simultaneousdigital square wave patterned transmission and simultaneous receive withsynchronous demodulation and pen capable, as shown in FIG. 23. Thissystem does not allow multi-mode concurrent touchscreen sampling, doesnot have true simultaneous sampling due to each row using a differentbit pattern which effectively scrambles the noise distribution onreceipt, is not capable of self-capacitance measurements, and due to theuse of square wave drive has a receive signal spectrum that contains theprimary frequency as well as its harmonics which necessitate lower traceimpedance to prevent attenuation of the higher harmonics across thepanel.

The systems shown do not allow multi-mode concurrent touchscreensampling, do not have true simultaneous sampling, use pulse or squarewave sampling which does not allows for anti-alias filtering and havehigh frequency components necessitating lower touchscreen impedances,and all but the last uses mux arrays with high parasitic capacitances.

Therefore, a need exists for a much faster sampling method that canacquire data simultaneously for different modes of, for example, self,mutual, and pen, and with simultaneous sampling of the differentchannels.

Also, in some applications, to reduce the sample time via signal tonoise ratio improvement where possible, continuous sampling schemes andadvanced filter methods, modulation and demodulation schemes, anddigital domain methods are needed. To keep the cost and power usage aslow as possible the circuitry should be as much in the digital realm aspossible.

Finally, many different touch sensors are now available that workthrough the measurement of changes to impedance, and providing a systemthat can handle multiple sensor types and configurations, includingthose currently known and those to be developed in the future, is alsogreatly desired.

SUMMARY

Circuitry, systems, and methods are provided that can acquire touchsensor data simultaneously for different modes of, for example, self,mutual, and pen, and with simultaneous sampling of the differentchannels. Drive/receive circuitry and methods of driving and receivingsensor electrode signals are provided that allow digital I/0 pins to beused to interface with touch sensor electrodes using external passivefilter components. Drive/receive circuitry is provided employing voltagefollowing sigma-delta A/D coverts that are adapted to both drive andsense touch sensor signals on multiple frequencies simultaneously. Thiscircuitry may be operated in modes to sense various combinations ofmutual, self, and pen touch signals simultaneously. While capacitivemulti-touch sensors are preferred, the circuits and methods herein areuseful with many other types of touch sensors as well.

Some embodiments are capable of utilizing semiconductor programmablelogic to simultaneously transmit and receive a plurality of frequenciessimultaneously on a plurality of channels giving longer sample windowsfor pen and self-capacitance signals, simultaneous self-capacitancesampling which makes external noise common mode to all data readings,simultaneous sampling of mutual capacitance makes external noise commonmode to all receive data, simultaneous sampling of mutual, self, penwith multiple pin solutions, low energy self-capacitance for finger/handproximity, low energy receive capability for Pen proximity, standardradio frequency processing for signal isolation, and reduced ditherlogic, among other solutions to prevalent problems in the touchscreenrealm.

Object of some embodiments of the present invention is to provide asystem directed to a digital realm multi-touch and pen system capable ofinterfacing to multiple touchscreen types, customization andimplementation in programmable logic hardware or fixed silicon, withimproved sampling capabilities and noise rejection capabilities.

Further, the drive circuit and method in some embodiments implement amixture of dither and self-capacitance carrier frequency to overcome thepotentially large hysteresis of the digital input 1-bit Sigma DeltaAnalog to Digital Converter when implemented on a digital input.

Further, the operation in some embodiments of the self-capacitance modewith all channels simultaneously allows for almost ideal self-capacitivesalt water rejection.

Further, the system in some embodiments can use advanced modulation anddemodulation schemes to reduce noise at or near the frequencies used todrive the different modes of function.

Further, the system in some embodiments is capable of driving andsampling a plurality of sensors and sensor types.

Further, the system in some embodiments is capable of dual or moremutual capacitive axis scanning using separate frequencies.

Further, the system in some embodiments is capable using a digital inputpin with settable transition reference or a differential analog typeinput pin with a comparator type circuitry.

Further, in some embodiments simultaneous sampling enables a method foridentification and removal of noise using linear or non-linear filteringnot possible with existing technology.

In view of the foregoing, some embodiments of the present inventionprovide a multi-touch system capable of greatly enhanced performance inspeed of function, resolution, sensitivity, immunity, and capability tohandle multiple types of input sensor configurations and input devicetypes.

These together with other objects and advantages which will becomesubsequently apparent reside in the details of construction andoperation as more fully hereinafter described and claimed, referencebeing had to the accompanying drawings forming a part hereof, whereinlike numerals refer to like parts throughout. Not all embodimentsprovide all of the advantages described above.

Some embodiments of the invention use digital channel driver hardwareand a single pole RC filter, the driver hardware and filter capable oftransmitting and receiving a multitude of frequencies into a variableimpedance sensor where changes to the impedance can be resolved on thedigital side of the driver to determine the relative change inimpedance.

Some embodiments of the present invention implement a digital to analogdrive method with good compatibility to existing field programmable gatearray hardware. Further, the drive method in some embodiments is ideallysuited towards continuous parallel sampling of the connected senseelements. Further, the drive method in some embodiments is capable ofsimultaneous driving and sampling the different modes ofself-capacitance, mutual capacitance, and receive/pen. Further, theoperation of the different modes allows for continuous sampling of selfand pen signals even during the mutual capacitance scan.

In one aspect of the present invention, touch sensor driver and receivercircuitry is provided for a multi-touch sensor, the circuitry including:multiple drive/receive circuits adapted to be coupled to respectivesingle row or column electrodes of the multi-touch sensor, eachcomprising a voltage-following sigma-delta A/D converter combined with asigma-delta D/A converter having a sigma-delta output filter for drivingeach respective row or column electrode, the voltage-following A/Dconverter connected to follow a reference signal on a first referencecomparator input by producing a feedback output at a virtual signal nodeon a second comparator input. The sigma-delta output filter alsoconnected to the virtual signal node. Drive signal generation circuitryis coupled to the reference comparator input of each of thedrive/receive circuits, operable to generate a mutual analog sensorsignal at a first frequency and a self-analog sensor signal at a secondfrequency different from the first frequency. The mutual analog sensorsignal may be coupled to other electrodes by mutual capacitive couplingor another type of mutual coupling. Some of the drive/receive circuitsare operable in a first mode to drive both said self and mutual signalssimultaneously to their respective electrodes, and to sense saidself-signal, and others of the drive/receive circuits are operable in asecond mode to drive said self-signal and sense both said self andmutual signals simultaneously from their respective electrodes. In someimplementations, the circuitry includes digital filter and demodulationcircuitry operable to separate and filter the simultaneously sensedmutual and self-signals. The drive and receive circuits may further beoperable in a mode to, in addition to their other functions,simultaneously sense a third pen analog sensor signal at a thirdfrequency different from the first and second frequencies, and thedigital filter circuitry is further operable to separate and filter thesimultaneously sensed pen analog sensor signal.

In some implementations, the respective drive/receive circuits includeone or more digital input pins of an FPGA device and one or more digitaloutput pins of the FPGA device, with an end analog filter connected toone of the one or more output pins, for removing high frequencycomponents and driving an analog voltage signal to its respective row orcolumn electrode. A digital portion of the drive/receive circuit isadapted to measure changes in the sensed driven signal caused by changesin the row or column electrode impedance via measuring internal changesin the digital portion of the drive circuit as it changes an outputdrive signal forcing the output to follow an input reference availableto a digital input. Several different versions are possible usingdifferent numbers of FPGA pins per channel; these may be done on ASICsas well but an ASIC would typically employ a one-pin solution. A 4-pin,FPGA version of the respective drive/receive circuits may include: anFPGA output pin for carrying the reference signal connected to a firstanalog filter together forming a sigma-delta D/A converter adapted toprovide an analog reference signal; an FPGA output pin configured to actas a sigma-delta A/D feedback pin connected to the virtual signal node;and two differential FPGA input pins, one connected to the first analogfilter output and the other connected to the virtual signal node. Athree-pin, FPGA version of the respective drive/receive circuits mayinclude: an FPGA output pin configured to act as a sigma-delta AIDfeedback pin; and two differential FPGA input pins, one connected to acommon analog reference signal and the other connected to the virtualsignal node. A two-pin, FPGA version of the respective drive/receivecircuits may include: an FPGA output pin configured to act as asigma-delta AID feedback pin; an FPGA input pin to the virtual signalnode, and having an internal reference voltage of the pin receiverconnected to a common analog reference signal. Also, a 1-pin version ofthe design may be constructed in which respective drive/receive circuitseach comprise FPGA or ASIC circuitry connected to a single pin coupledto the respective row or column electrode, and external analog filtercomponents coupled to the single pin.

In some implementations, the circuitry further includes digitalmodulation circuitry configured for modulating the self-sensor signalsfor rejecting continuous interfering signals at the first frequency. Thecircuitry may reject common mode noise by being adapted to subtract thecommon-mode proportional noise based on the simultaneously sensed selfand mutual signals.

In some implementations of the circuitry, the voltage-followingsigma-delta A/D converter is constructed with the comparator inputscomprising a differential digital input circuit connected to twointegrated circuit pins.

In another aspect of the invention, a method is provided for driving andreceiving signals to and from a multi-touch sensor, the methodincluding: (a) for each of a first group of electrodes comprising row orcolumn electrodes of the multi-touch sensor, sequentially scanning amutual analog sensor signal through the group of electrodes by feedingit to respective sigma-delta D/A converters connected to the respectiveelectrodes, the mutual analog sensor signal comprising a firstfrequency; (b) while performing (a), for each of a second group ofelectrodes comprising row electrodes or column electrodes of themulti-touch sensor, simultaneously driving a self-analog sensor signalthrough a sigma-delta D/A converter onto pins coupled to the respectiverow electrodes or column electrodes, the respective self-analog sensorsignals comprising a second frequency or a data pattern modulated at asecond frequency; and (c) for each of the second group of electrodesused in (b), simultaneously sampling touch sensor data for at least twodifferent modes of self and mutual, the touch sensor data comprisingsensed altered sensor signals at the first and second frequencies,altered by the impedance of the row or column electrodes.

In some implementations, of this method, the simultaneous sampling isperformed by a voltage following sigma delta A/D converter integratedwith each sigma-delta D/A converter driving the respective row or columnelectrodes, the voltage following A/D converter having a comparator witha first reference comparator input and a second comparator input, thefirst reference comparator input receiving the self-analog sensor signaland the second comparator input connected to the sigma-delta D/Aconverter output.

In some implementations of this method, a pen is sensed by performing aspart of step (c) for each of the first group of electrodes and thesecond group of electrodes, simultaneously sampling a third pen analogsensor signal a third transmitted from a pen at a third frequencydifferent from the first and second frequencies.

In some implementations, the method further includes (d) for each of therows or columns that are not driven in (b) with the mutual analog sensorsignal, scanning a second mutual analog sensor signal sequentiallythrough respective sigma-delta D/A converters onto pins coupled to therespective row or column electrodes, the second mutual analog sensorsignal comprising a fourth frequency different from the first and secondfrequencies and different from a third pen frequency if a pen frequencyis employed in the method; and (e) for each of the rows or columns thatare driven in (b), simultaneously sampling touch sensor data for atleast two different modes of self and mutual, the touch sensor datacomprising received altered sensor signals at the second and fourthfrequencies. In some implementations, the self-analog sensor signalscomprise a carrier wave modulated with a 50% duty cycle digital signalfor rejecting continuous interfering signals at the first frequency. Themethod may further include subtracting common-mode proportional noisebased on the simultaneously sampled self and mutual touch sensor data.

In some implementations, the method may also include adjusting thefrequency of the self-analog sensor signals or the mutual analog sensorsignals by controlling a digital frequency generator. The self-analogsensor signal, mutual analog sensor signal, and pen analog sensor signalmay include multiple frequencies, which are typically grouped for eachsignal for ease of demodulation. In the case of the pen, multiplefrequencies may be transmitted into the sensor array from multiple penelectrodes and received in the manner described herein.

In another aspect of the invention, a method is provided for driving andreceiving signals to and from a multi-touch sensor, the methodincluding: (a) for each of a first group of electrodes comprising row orcolumn electrodes of the multi-touch sensor, sequentially scanning amutual analog sensor signal through the group of electrodes by feedingit to respective sigma-delta D/A converters connected to the respectiveelectrodes, the mutual analog sensor signal including one or more firstfrequencies; (b) for each of a second group of electrodes comprising rowelectrodes or column electrodes of the multi-touch sensor sensing touchsensor mutual data, the touch sensor mutual data comprising sensedaltered sensor signals at the one or more first frequencies, altered bycoupling between the row and column electrodes; (c) simultaneously tothe sensing of (b) for each of the second group of electrodes,simultaneously sampling a pen analog sensor signal transmitted from apen at one or more pen frequencies different from the first frequenciesusing the same A/D converter performing the sensing of (b). The pensignaling may include multiple electrodes transmitting multiple signalsfrom the pen on different frequencies, which is referred to as one ormore pen frequencies to identify that a single pen frequency may be usedor many.

In some implementations of this method, the simultaneous sampling isperformed by a voltage following sigma-delta A/D converter integratedwith each sigma-delta D/A converter driving the respective row or columnelectrodes, the voltage following A/D converter having a comparator witha first reference comparator input and a second comparator input, thesecond comparator input being connected to the sigma-delta D/A converteroutput.

In another aspect of the invention, a drive/receive circuit is providedwhich is adapted to be coupled to a single row or column electrodes of amulti-touch sensor, the circuit including a voltage-followingsigma-delta A/D converter combined with a sigma-delta D/A converterhaving a sigma-delta output filter for driving the row or columnelectrode, the voltage-following A/D converter connected to follow areference signal on a first reference comparator input by producing afeedback output at a virtual signal node on a second comparator input,the sigma-delta output filter also connected to the virtual signal node.Also included is drive signal generation circuitry coupled to thereference comparator input of the drive/receive circuit, and operable togenerate a mutual analog sensor signal at a first frequency and aself-analog sensor signal at a second frequency different from the firstfrequency. The drive/receive circuit is operable in a first mode todrive a mutual signal to the electrode, and operable in a second mode tosense said mutual signal from the electrode.

In some implementations, the drive signal generation circuitry isfurther operable in the first mode to simultaneously generate aself-analog sensor signal at a second frequency different from the firstfrequency, and to simultaneously sense said self-signal. In someimplementations, the same self-sensing scheme may be provided in thesecond mode. The drive signal generation circuitry may also be furtheroperable in both modes to simultaneously sense a third pen analog sensorsignal at a third frequency different from the first and secondfrequencies. In some implementations, the circuit may further includedigital filter circuitry and demodulation circuitry further operable toseparate and filter the simultaneously sensed pen analog sensor signal.In various aspects of the present invention, the following features areprovided that may be employed alone or in combination to achieveimproved touch sensor circuits, systems, and methods.

A multi-touch sensor and electrostatic digitizing pen system is providedcomprising a flexible programmable logic block and driver circuitembedded in a semiconductor utilizing a method of simultaneous transmitand receives, simultaneously on a plurality of channels with asimultaneous plurality of frequencies resulting in vastly improvedperformance.

A multi-touch system is provided for one or more of improving speed,efficiency, transceiver channel separation, and noise rejection, throughthe use of simultaneous and continuous sampling of multiple channels atmultiple frequencies to enable heretofore independently operatedtouchscreen modes to be operated now concurrently.

Multi-touch system drive channels are provided capable of simultaneousmultiple modes such as self-capacitance, mutual capacitance transmit orreceive, and receive, using a digital input or using a digital inputwith analog capable reference, or analog comparator type input withinternal logic, analog filter components, pulse width modulation logic,digital filter components, modulation and demodulation logic, and ditherlogic; comprising a voltage following Sigma Delta Analog to DigitalConverter drive.

A multi-touch system is provided that is capable of a plurality ofsensors and sensor types through configuration of the drive modulationand demodulation scheme which is not limited to single frequencies orchannels and can therefore be configured to match characteristics ofdifferent types of hardware such as projected capacitance touchscreens,electrostatic pens, resistive touchscreens, pressure sensitivetouchscreens, strain gauge touchscreens, or any sensor requiring a drivesignal where impedance changes to the sensor are measured to determinesensor action.

A multi-touch system is provided capable of receiving an externallygenerated signal at some frequency and demodulating signals on saidincoming frequency with Phase Shift Keying (PSK), Frequency Shift Keying(FSK), Quadrature Amplitude Modulation (QAM) or other demodulationscheme during independent read only mode or simultaneously with othersampling and driving modes.

A multi-touch system is provided capable of single axis or dual axismutual capacitive scanning mode operation during independent mutualcapacitive mode or simultaneously with other sampling and driving modes.

A multi-touch system is provided with improved self-capacitance modeacquisition for improved conductive contaminant (salt water rejection)identification and rejection, and improved spatial projection distancevia simultaneous drive and measurement of all touchscreen channels thusforcing the change in signal due to touch coupling to be via the usersground path and not through changes in channel to channel touchscreenimpedance changes.

A multi-touch system is provided with improved sample resolution via useof noise shaped dither in combination with the continuous low frequencyand low amplitude self-capacitive signal used as the reference or aspart of the reference to overcome hysteresis and quantization on theself-capacitance mode signals as well for other signals of interestconcurrently in operation at the time such as the mutual capacitancereceive and or pen receive signals.

A multi-touch system is provided that generates and uses dither signalscapable of using a shared bit rolled dither: a single dither signalshared between all channels with or without a delay difference betweenchannels: to randomize dither noise across system channels enhancingdither noise randomization and smoothing of energy across channels or tosynchronize dither noise across system channels to enhance simultaneousnoise rejection by keeping all channels as similar as possible.

A multi-touch system is provided using all digital processing and drivechannels utilizing one or more digital output pins and one or moredigital input pins with an end analog filter on the output pin to removehigh frequency components thereby enabling an analog voltage signal todrive a sensor where the sensor has some impedance change that affectsthe signal's properties such as phase, amplitude, frequency, or offsetvoltage and the change can be measured via the internal changes in thedigital portion of the drive circuit as it changes the output drivesignals forcing the output to follow an input reference available to thedigital input which may be comprised of stationary or changing signals.

A multi-touch system is provided using all digital processing and drivechannels utilizing one or more digital output pins and or one or moreanalog comparator input pins with an end analog filter on the output pinto remove high frequency components thereby enabling an analog voltagesignal to drive a sensor where the sensor has some impedance change thataffects the signal's properties such as phase, amplitude, frequency, oroffset voltage and the change can be measured via the internal changesin the digital portion of the drive circuit as it changes the outputdrive signals forcing the output to follow an input reference availableto the analog input which may be comprised of stationary or changingsignals.

A multi-touch system is provided where most or all of the digital andanalog circuitry is internal to the silicon using a single pin toconnect to the sensor channel.

A multi-touch multi sensor system is provided using substantiallyparallel simultaneously active drive circuitry and system logic that canbe implemented and made operable in present day field programmable gatearray hardware.

A method is provided for synchronous modulation demodulation on a touchscreen system using PSK, FSK, or other advanced modulation schemes wherephase and or frequency changes are incorporated into the modulation ofthe output signal and also then to the demodulation of the input streamto achieve a final demodulated coherent synchronous signal with enhancedsame frequency rejection.

A method is provided for synchronous modulation demodulation on a touchscreen system using sweeping, hopping, chirp, or any changing signalpattern incorporated into the modulation of the output signal and alsothen to the demodulation of the input stream to achieve a finaldemodulation coherent synchronous signal with enhanced frequencyrejection.

A method is provided for identification and removal of noise using thesimultaneous sampling properties of the parallel channel drivers andconcurrent mode properties of the system.

In some versions, the touch sensor itself is included with theinvention, while in others the drive and receive circuitry and methodsmay be embodied in a touch sensor controller chip or other integratedchip (IC) for interfacing with a touch sensor such as those used withtouchscreens on smartphones, tablets, notebook PCs, point-of-salekiosks, touch sensitive fabric, touch sensitive surfaces, drawing padsor pen input pads, and other any other touch sensor array products.Further, the drive/receive circuits disclosed herein may be used withnon-array sensors such as touch sensitive buttons or other sensors;however touch sensor arrays are the most beneficial application. In someversions, the circuitry and method may be embodied in IC design coressuch as VHDL or other FPGA or ASIC licensed intellectual property cores.In such cases, the invention is embodied in the computer readableinstructions executable to program a hardware device to embody theintegrated circuit designs described herein, or to embody integratedcircuit designs for performing the methods herein. In other words, thescope of this patent cannot be avoided merely by preparing and making,using, selling, or importing an intellectual property design core thatembodies the designs or methods herein. Each of the designs andprocesses below may be embodied in a combination of circuit designinformation or executable code to be executable by a controller incombination with such a circuit.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

FIG. 1 is a block diagram of an embodiment of a touchscreen controlsystem including touchscreen drive and receive circuitry built withdigital configured to transmit or receive multiple modes simultaneously.

FIG. 2 is a supporting legend for FIGS. 2-6 and FIGS. 15-16.

FIG. 3 is a diagram of an embodiment of a simultaneous drive methodshowing a multi-mode state (Self+Receive) and indicating in notes thedifferent pin configurations capable of achieving such.

FIG. 4 is a diagram of an embodiment of a simultaneous drive methodshowing a multi-mode state (Self+Receive+Mutual Scan) and indicating innotes the different pin configurations capable of achieving such.

FIG. 5 is a diagram of an embodiment of a simultaneous drive methodshowing a multi-mode state (Receive+Mutual Scan) and indicating in notesthe different pin configurations capable of achieving such.

FIG. 6 is a diagram an embodiment of a simultaneous drive method showinga multi-mode state (Self+Receive+Mutual Scan) and indicating thedifferent pin configurations capable of achieving such.

FIG. 7 is a block diagram of a channel driver and receiver circuitaccording to some embodiments of the invention.

FIG. 8A is a schematic diagram showing an embodiment of a 2-pinconfiguration drive/receive circuit.

FIG. 8B is a schematic diagram showing an embodiment of a 3-pinconfiguration drive/receive circuit.

FIG. 9 is a schematic diagram showing an embodiment of a 4-pinconfiguration drive/receive circuit.

FIG. 10 is a schematic diagram showing an embodiment of a drive/receivecircuit in a 2-pin configuration of programmable logic with specialrequirements that may not be available in present generationprogrammable logic.

FIG. 11 is a schematic diagram showing an embodiment of a drive/receivecircuit in a 1-pin configuration of programmable logic with specialrequirements.

FIG. 12 is a block diagram showing an embodiment of a CIC (cascadedintegrator-comb) Filter/Decimation/Demodulation/Amp/Phase sample chainshowing resolution of three different simultaneous frequenciesrepresenting three separate modes of touchscreen function.

FIG. 13 is a diagram showing the resultant signal energies from bothhuman contact and the pen digitizer which are all sampled in the same 5mS frame.

FIG. 14 is a timing diagram showing a single capture frame withsimultaneous Self, Pen, and Mutual scan for FIG. 13.

FIG. 15 is diagram showing an embodiment of a simultaneous drive methodshowing a multi-mode state (Self+Receive+Dual Mutual Scan) andindicating the different pin configurations capable of achieving such.

FIG. 16 is a diagram showing prior art self-capacitance measurement withshielding elements and the same measure made on a system of the currentinvention with all elements simultaneously driven.

FIG. 17 is a diagram showing a phase modulation scheme to rejectcontinuous interfering signals at the target frequency.

FIG. 18 is a 3rd Order, 400 MHz., 100 decimation CIC filter.

FIG. 19 is a simple simulated example of the drive channel signalsshowing the drive, dither, and voltage following (sensed) signals.

FIGS. 20-23 show prior art circuits discussed in the background.

DETAILED DESCRIPTION OF THE INVENTION

Novel features believed to be characteristic of the various inventions,together with further advantages thereof, will be better understood fromthe following description considered in connection with the accompanyingdrawings in which preferred embodiments of the present invention isillustrated by way of example. It is to be expressly understood,however, that the drawings are for the purpose of illustration anddescription only and are not intended to define the limits of theinvention.

FIG. 1 is a block diagram of an embodiment of a touchscreen controlsystem including touchscreen drive and receive circuitry 10 constructedwith flexible programmable logic embedded in a semiconductor devicewhich may be a touchscreen controller chip, or may be integrated into alarger system on chip arrangement with other system functionality aswell. Typically, the circuitry appears in touchscreen or other touchsensor controller circuitry. The circuitry 10 transmits and receivessimultaneously on a plurality of channels 12 to drive analog sensorsignals through channel drivers 30 to the electrodes of a multi-touchsensor 14. The electrodes typically include row and column electrodesarranged in a grid, but may include other nonsymmetrical arrangements ofelectrodes, multiple grids, or other suitable arrangements of electrodesthat can cross-couple signals in response to touch or proximity. Theanalog sensor signals are driven at a plurality of simultaneousfrequencies 16 in accordance with some embodiments of the presentinvention. While four channel drivers are shown in the drawing, this isto illustrate a plurality, and the preferred versions will have as manychannels as there are touchscreen electrodes (rows and columns), withrepeated instantiations of the drive module, including drive circuitryand receiving filters, for each channel. The diagram generally shows thedigital clock domains and their functionality, the Drive Module Array,the System Logic Blocks, the Demod Logic Blocks, and the Processor andMemory Logic Blocks. The processor also includes program memory forstoring executable program code to control and direct the variousdigital logic and digital signal processing functions described herein.

As can be seen in the diagram of FIG. 1, the system touchscreen driverand sensor circuitry can be embodied in an FPGA or ASIC. Someembodiments provide a multitouch system FIG. 1 with flexibleconfiguration. Some embodiments provide a multi-touch system capable ofoperating almost exclusively in the digital realm, as described below,meaning that an FPGA or other reconfigurable or programmable logicdevice (PLD) may be employed to construct almost the entire circuit,without the need for op amps or other active external analog components,beyond the driver circuitry included in the FPGA or PLD. Externalresistors and capacitors 18 are all that are needed to supplement thedigital I/O circuits of an FPGA to achieve the channel drive/receivecircuits in preferred embodiments. This is because of the unique use ofsigma-delta converter combinations that allow the digital I/O pins toact in a way similar to analog sensor drivers. Some embodiments providesystem implementation and operation in programmable logic or customsilicon.

The other parts of the system block diagram of FIG. 1 include,generally, the lowpass filter/decimator block 18 that filters theincoming sensed signals, the system logic blocks 20, the demodulationlogic blocks 22, and the processor and memory logic blocks 24, whichwill all be further described below. Most of the benefits of theimproved touch sensor driving circuitry and control schemes come fromthe design of the drive/receive circuit itself, and the use of it todrive and receive different types of signals in a flexible andreconfigurable manner. Preferably the drive/receive circuitry drivingthe various touch sensor electrode channels is embodied in a digitaldevice and drives and receives signals using digital I/O drivers andreceivers, but in some versions analog amplifiers or other analogcomponents may be employed with the signaling schemes described herein.This design may be referred to herein as a “digital channel driver 30”,“channel driver 30,” and “drive/receive circuit 30.” Several variationsof the channel driver will be described below, followed by a descriptionof several unique and beneficial signaling and measurement schemes thatadvance the ability to accurately measure touch on many types of touchsensors. The Digital Channel Driver:

Some embodiments of the invention use digital channel driver hardwareand a single pole RC filter capable of transmitting and receiving amultitude of frequencies into a variable impedance sensor where changesto the impedance can be resolved on the digital side of the driver todetermine the relative change in impedance from each sensor electrode.

Such impedance changes may manifest in several ways. A change ofcapacitance in a floating sensor system, when driven by a sine wave,will present as a phase change. A change in resistance in a floatingsensor system will also cause a phase change, finally a resistance loadchange in a resistive sensor system will cause a DC offset change. Thesechanges are changes between the generated reference signal (AC and/orDC) and the generated analog feedback signal which is an averagedrepresentation of the digital stream of “higher/lower” signals from the1-bit ADC.

Some embodiments employ said channel drivers to interface to multipletypes of sensors such as projected capacitance touchscreens, resistivetouchscreens, pressure sensitive touchscreens, strain-gauge arraytouchscreens, etc.

Some embodiments of the invention use said channel drivers in a parallelmanner to drive touchscreens 14 or other touch sensor arrays with signalcombinations allowing multiple mode simultaneous touchscreen sampling(self, mutual, and receive). Such ability requires the channel driver tobe capable of a minimum of transmitting a single continuous frequency(self), transmitting an intermittent frequency (mutual TX), receiving afrequency (mutual RX), and receiving pen frequencies all through asingle Delta Sigma Driver at the same instance and also handling thefilter, decimation, and demodulation. Typically, these signals aregenerated and mixed, or generated directly, or generated and channeled,then sent into the reference of the Sigma Delta 1-bit ADC.

Some embodiments of the invention use said parallel channel drivers withdither signals combined with a low amplitude self-capacitance modesignal to overcome input hysteresis of the digital I/O pins employed inthe drive/receive circuits 30, and allow continuous self-capacitive modesignal sampling and associated signal processing improvements, such asthat described with respect to FIG. 19. By using a low frequencycontinuous working signal (the self-capacitance signal) that drive theone-bit digital ADC above and below its hysteresis band, the requirementfor lower amplitude high frequency noise dithering is reduced for thesignals received on the channel (mutual RX and Pen-generated analogsensor signals).

Some embodiments of the invention employ said parallel channel driversto provide a capability of improved conductive contaminant (such as, forexample, salt water) rejection through the self-capacitive mode methodof driving all channels simultaneously to eliminate unwanted impedancepaths from channel to channel allowing only impedance changes due to theuser's touch and ground path.

The operation of the self-capacitance mode with all channels drivensimultaneously allows for almost ideal self-capacitive salt waterrejection operation due to the fact that the change to variableimpedance paths happen through the users touch to ground only andchanges to the impedance paths back to the touchscreen are almostzeroed. This is as close as a continuous plane driven at the frequencyof interest, as possible.

FIG. 7 is a circuit block diagram of drive/receive circuitry for achannel driver according to some embodiments. Some embodiments of theinvention use a hardware array of one or more channel drivers 30, asdepicted generally by the components in the dotted line numbered 30, todrive and receive analog sensor signals to a sensor. Each channel driver30 generally includes a novel voltage following sigma-delta A/Dconverter that includes: a sigma delta D/A converter comprised of asigma delta driver 36 driving a digital output to which is connected asigma-delta output filter 38, which typically an analog single pole RCfilter. The A/D converter portion of the circuit is implemented with asigma-delta comparator 34 having two inputs, one connected to thesigma-delta output filter node which drives the touch sensor electrode40. A second EMI filter 39 may also be used to filter high frequencynoise at the electrode 40.

The other input of the sigma-delta comparator, the reference input, isconnected to an analog sensor drive signal 35, which contains the one ormore analog frequencies (which may be modulated signals) employed todrive the touch sensor in various modes as discussed below. Sensor drivesignal 35 is shown bridging the integrated circuit 11 and the externalcomponents because, while the signal is typically generated on theintegrated circuit in digital form, it may be driven outside through D/Aoutputs in some versions, or it may be fed into the integrated circuitas a reference voltage where system design allows, as will be furtherdiscussed with respect to various versions of the circuit below. Thesensor drive signal in this version is generated by drive signalgeneration circuitry 41. This typically includes, as further describedbelow, digital frequency generating, and mixing the digital signals incases where multiple signals are transmitted simultaneously. Referringnow this version of the analog sensor drive signal 35, this signalproduced by drive signal generation circuitry 41 feeding the referenceof each of the drive/receive circuits 30, and operable to generate amutual sensor signal (or “mutual signal”) at a first frequency and aself-sensor signal (or “self-signal”) at a second frequency differentfrom the first frequency. The self and mutual sensor signals driving theelectrodes for detecting self (same electrode) impedance changes andmutual (cross coupled from other electrodes) impedance changes are firstgenerated digitally at respective frequency generators, which preferablygenerate sine waves at the respective frequencies f1 and f2, but maygenerate other continuously varying signals such as wavelet sequences,modulated waves, or other analog varying patterns. While generally thevarious signals are discussed as being at specific frequencies, they mayalso be a group of sub-signals carried on a set of frequencies, whichwill be driven together, or transmitted together in the case of the pensignal. The pen signal may include multiple electrodes transmittingmultiple signals from the pen on different frequencies, which isreferred to as one or more pen frequencies to identify that a single penfrequency may be used or many. Dither is also added for the reasonsdiscussed herein. It is noted that one special case of this circuit iswhen the self-analog sensor signal is not used, and the circuit isemployed only to receive a pen analog sensor signal on a thirdfrequency, and to transmit the mutual analog sensor signal and, at othernodes, to receive the mutual analog sensor signal. In such case, thedither is still added to the mutual analog sensor signal. As shown, theanalog sensor drive signal 35 is connected to the second comparatorinput, which functions as a voltage follower due to the feedbackconnection of the sigma-delta driver 36 to the first comparator 34 inputat node 37. This connection enables the drive/receive circuit 30 to actas a sigma-delta analog to digital transceiver. That is, circuit 30 bothdrives the signal present on reference 35 out through the sigma-deltadriver portion, and to sense or receive the driven signal changes neededto follow the reference 35—which indicate the impedance changes causedby touch on the touch circuitry, or signal or noise external to theelectrode, such as the mutual analog sensor signal and the pen sensorsignal(s). The feedback connection at node 37 causes this node to act asa “virtual signal” node, which the entire voltage following A/Dconverter attempts to match to analog sensor drive signal 35. Becausethe impedance of touch sensor electrode 40 changes when touched based oncapacitance, inductance, or resistance changes, the signal at virtualsignal node 37 contains variations indicating such changes, as thesigma-delta D/A converter portion of the circuit drives more or lessvoltage to node 37 to keep up with the impedance changes. These changesare present in the comparator output signal at node 33, which isfiltered and decimated to a lower digital sample rate at block 18, forprocessing by the system internal logic, such as that shown in FIG. 1,to detect and process the various touch and pen inputs. The voltagefollower circuit also works to detect signals coupled into the sensorelectrode 40, such as analog signals generated from a touchscreen pen,or mutual-coupled signals driven on other touch sensor electrodes andcoupled into the electrode detecting the signal. The depicted circuit istherefore adapted to drive one or more analog signals, and sense one ormore analog signals, at the same time by mixing the desired sensorsignals to be driven into sensor drive signal 35, as will be furtherdescribed below.

While a sigma-delta based channel drive/receive circuit is shown here inthe preferred version to employ only digital I/O pins and not requireanalog op amps or analog A/D and D/A converters or switches, this is notlimiting and other versions may employ such analog components, both onand off the integrated circuit. For example, the A/D converter portionof the circuit may be comprised of a digital input with an AC capablegenerated reference threshold or an analog comparator with one inputaccepting an AC capable generated reference.

Recently, much work on sigma-delta AID converters has been done with thegoal of producing a high frequency high resolution solution capable ofreplacing the more standard analog versions of A/D converters such assuccessive-approximation, integrating, and Wilkinson ADC. Much work hasbeen directed towards accuracy and improvements in linearity. In thepresent invention resolution, speed, and repeatability are the keyfeatures required for successful touchscreen function. Standing alone, asimple Sigma Delta ADC, without accuracy and linearity, will find veryfew applications. Coupled to the concurrent driving modes andsimultaneous sampling of the present invention as well as internalcalibration of the touch system, these and other limitations of thesigma-delta ADC become trivial issues to the system operation. Thesigma-delta driver and sensor designs herein are much less sensitive tononlinearity, low input impedance, and accuracy issues than typicalapplications of such ADC designs.

As employed in some embodiments herein, the touchscreen driver andreceiver circuitry includes a hardware array of channel drivers 30 suchas that of FIG. 7, with internal logic operating on a high frequencyclock 32. The digital input and output logic if allowed to run freecould switch and oscillate up to the capabilities of the siliconhardware possibly producing very high unwanted frequencies. The loop iscontrolled and limited to a known frequency via the clocked flip-flop 31which is set to a speed compatible with the silicon hardware and of avalue favorable to external filtering and internal resolution.

Some versions of the touchscreen driver and receiver circuitry hereinalso include a hardware array of channel drivers utilizing a filter anddecimation chain to move the data from the high frequency low resolutionrealm of the one-bit sigma delta A/D converter to the low frequency highresolution realm of function needed for further signal processing.

FIG. 11 is a schematic diagram showing an embodiment of the circuit ofFIG. 7, implemented using one pin of a programmable logic device, withspecial requirements that may require customization of presentgeneration of programmable logic I/O circuitry. The preferred embodimentof the channel driver depicted in FIG. 11 uses a single pin, labeled 1,per channel and functions without any limitation as to the mutualtransmit mode as discussed herein, but may require custom silicon at thepresent time due to the need for internal analog channels, analogswitches, output and input buffer simultaneous function, and also higherdigital buffer output impedance settings more in line with use withsmaller output filter capacitance C1. Current output buffer impedancenear the range of <1000 ohms where 5 k to 10 k ohm would allow muchsmaller C1 values. For FPGA solutions that provide such features, onlycustom configuration, and not custom circuit modification, are requiredto achieve the depicted design.

The depicted circuit includes a channel driver and receiver circuitry30, with the internal or onboard portions of circuitry 30 (on the IC)identified by block 11, and the sigma-delta output filter 38 implementedwith an internal resistor R1, and an external capacitor C1. The portionlabeled “Drive Module” represents the internal portions of the drivechannel circuit, which are repeated for each channel. The EMI filter 39is implemented with external resistors and capacitors as shown. EMIfilter 39, in this example, is a lowpass RC filter with a cutofffrequency of approximately 1 Mhz. Filter 39 functions to reduce theoutgoing noise from dither, the PWM signal noise, and clock EMI that mayemanate from channel driver 30. It also functions to reduce EMI(electromagnetic interference) from the sensor electrode, and to reduceESD (electrostatic discharge) noise coming in from the sensor electrode.The sigma-delta driver circuit 36 is implemented with the digital outputdriver for pin 1, which is connected to both the external portions ofthe sigma-delta filter, and connected back to the voltage following AIDcircuit input. The voltage following sigma-delta AID circuit includescomparator 34, which in this embodiment is implemented with thecomparative input receiver of the built-in drive receive circuitry ofthe IC. In this version the comparator of circuit 34 is fed with analogsensor drive signal 35. The comparator 34 output is fed to flip-flop 31,where it is clocked through with the local, high frequency clock signalCLK to control the sampling rate of the signal passed through to theflip-flop 31 output 33. This output 33 carries the high-frequencydigital received signal which is passed to the CIC filer and decimator18, and also fed back to the sigma-delta driver 36 as a feedback signal.Using such feedback to receive the analog signal at virtual signal node37, while driving the comparator reference input with the analog sensordrive signal 35, provides the voltage following A/D converter isconnected to follow a reference signal on a first input by producing afeedback output at a virtual signal node on a second input, thesigma-delta output filter also connected to the virtual signal node 37to drive the sensor electrode.

The received signal at node 33 is lowpass filtered and decimated to alower sampling rate at CIC and decimator 18. While a CIC filter is usedhere, this is not limiting and any suitable lowpass digital filterarrangement may be used. The output of filter and decimator 18 is fed tothe demodulation logic blocks (FIG. 1), where it is processed andinterpreted to detect touch inputs on the touch sensor electrodes.

Referring now to the analog sensor drive signal 35, this signal isproduced by drive signal generation circuitry 41 feeding the referenceof each of the drive/receive circuits 30 operable to generate a mutualsensor signal (or “mutual signal”) at a first frequency and aself-sensor signal (or “self-signal”) at a second frequency differentfrom the first frequency.

The self and mutual sensor signals driving the electrodes for detectingself (same electrode) impedance changes and mutual (cross coupled fromother electrodes) impedance changes are first generated digitally atrespective frequency generators 42, which preferably generate sine wavesat the respective frequencies f1 and f2, but may generate othercontinuously varying signals such as wavelet sequences, modulated waves,or other analog varying patterns. For example, one or more of the f1, f2and f3 signals may include groups of frequencies, such as three sinewave frequencies, in which the received magnitudes are accumulatedtogether after demodulation. Frequency sweeping, hopping, or chirpingmethods may also be used with the analog signals of the f2, f1, and f3(Self, Mutual, Pen) measurements. Prior art techniques that employsquare waves for the sensor signals are generally not the best selectionfor these signals because the square waves contain harmonics which causedeleterious effects when they pass through the sensor electrodes, andthe sensor measurement is not available across the entire period of thewave. This version generates sine waves at the f1 and f2 frequencies,which are sufficient different frequencies that they can be easilydemodulated separately or separated by filters in the receiver logicportions of the system. The self-sensor signal is fed to a dithercircuit which adds dither to the signal to improve the resolution andovercome hysteresis issues in the A/D converter portion of circuit 30,as further described below. A common dither may be added to allself-sensor signals, or independently generated dithers may be used. Thedithered self-sensor signal is added to the mutual sensor signal atadder 44. Dither as used herein is the addition of a low magnitude noisesignal, typically shaped in the frequency domain to cover a desiredbandwidth. The frequency components of the noise are usually selected tobe above the final usable system frequency range, and the noisetherefore gets filtered out of final readings. Dither noise is oftenadded to A/D systems to improve resolution by breaking up quantizationnoise (step noise). Herein it is also used to overcome the 1-bit A/Dhysteresis by randomly pushing the input voltage below and above thehysteresis band exhibited by the comparator circuit. After dither isadded to the signal shown, the two branches are then separated PWM(pulse width modulation) modulated at PWM modulators 45. Then, the PWMsignals pass to a sigma-delta DIA converter implemented with a digitaloutput driver 46 (having an internal resistance) and a sigma-deltaoutput capacitor 47. The output of these two D/A converters is then ananalog dithered self-signal at f2 frequency and a combined analog selfand mutual signal having f1 and f2 added. These signals may be routed tofeed other channel drive/receive circuits as depicted, to avoidduplicating the signal generation circuitry and to provide drive signalsat a common phase. Analog switch or multiplexor 48 provides the abilityto control whether the drive/receive circuitry 30 drives both self andmutual signals, or only the self-signal at f2. This enables selection ofmodes and the mutual scanning function described below. The self anddither may be set to zero to provide a pure mutual signal at frequencyf1 should the sensing scheme employed with a particular design requireonly the mutual signal to be driven at some point. It should be notedthat while the depicted circuit generates analog versions of both theself and mutual signals, some versions may include a control selectionswitch feeding only one D/A converter, selecting the mode of f2 or f1+f2before converting the signal to analog (the version of FIG. 9 has such adesign). Each drive/receive module may also generate their own self,mutual, or self and mutual signals, but such a design needlesslyreplicates the signal generation circuitry. For versions in whichseparate mutual frequencies are desired for each row, each drive receivecircuit 30 may be fed with a separate mutual signal, driven at otherfrequencies such as f4, f5, f6, . . . fn, up to the number of rows orcolumns that are used for mutually coupled signal detection. Thus, thefull range of driving and receiving schemes discussed herein, includingthe driving processes of FIG. 6 and FIG. 15 may be applied with thisembodiment.

The output of drive signal generation circuitry 41 is the analog sensordrive signal 35, which is fed to the reference input of comparator 34,part of the voltage following sigma-delta A/D converter. This circuitacts both to drive the sensor electrode, which can be done directly orthrough a filter 39, and to sense changes of the sensor electrodeimpedance as discussed above. The circuit, and the other versionsdescribed herein, can also receive other signals coupled into the sensorelectrode, such as mutual signals coupled from other electrodes, or apen signal coupled directly into the connected electrode by an activepen used with the touch sensor array.

The circuit of FIG. 11 is preferred because it uses fewer output pins,only one per drive/receive channel, and so an array of such circuitsdriving approximately 100 I/O pins of the integrated circuit may beemployed to drive a 50-row by 50-column touch sensor such as atouchscreen, touch pad, or touch sensitive fabric using PEDOT variableresistive electrodes. However, implementing the circuit of FIG. 11 andother 1-pin equivalents thereof on an FPGA platform requires first acomparative input and digital output for each I/O pin employed, second adigital output impedance at driver 36 high enough for the requiredsigma-delta output filter at C1 (which output impedance is preferably inthe range of 1 k Ohms to 10 k Ohms), and third, control over the analogvoltage references (feeding the vref of input comparators) and otheranalog components such as analog switches. Some present FPGA productsmay allow such control, while others do not. Therefore, a custom ASIC ora customized FPGA product is needed in some cases to achieve the circuitof FIG. 11. The different transmit receive modes herein, including thoseof FIG. 3, FIG. 4, FIG. 5, FIG. 6 and FIG. 15 may be applied with thisembodiment.

Another embodiment of the channel driver FIG. 10 uses two pins perchannel and functions without the mutual transmit mode limitationsdiscussed herein with respect to some other embodiments. It does notrequire internal analog channels and switches as the embodiment of FIG.11 does, but may still require custom silicon at the present time due tothe need for output and input buffer simultaneous function and alsohigher digital buffer output impedance. The depicted embodiment of FIG.10 functions similarly to the version in FIG. 11, but employs two pins 1and 2, and uses an external capacitor C2 external for the sigma-deltaoutput capacitor 47 of the single sigma delta D/A converter for thesensor drive signal, made up of driver 46 and capacitor 47. The drivesignal generation circuitry 41 also includes the driver 46 and externalcapacitor 47. This capacitor 47 is connected to the pin to filter thesigma-delta D/A conversion, and the resulting signal 35 is routedinternally from the pin to the comparator 34 reference input, similarlyto the design of FIG. 11. The depicted design may be used where on-chipcapacitors are not available near the drivers. This design selectsbetween the sensor signals of f2 or f1+f2 with a digital switch 48rather than an analog switch. Alternately, the signal to be driven maybe generated directly without the need for a selection switch, howeverthis scheme provides ability to feed other drive/receive circuits withthe digital versions of the two drive signals and avoid duplicating mostof the drive signal generation circuitry 41. The requirements to usethis design with an FPGA implementation are first a comparative inputand digital output for each I/O pin employed, second a digital outputimpedance at driver 36 high enough for the required sigma-delta outputfilter at C1. The different transmit receive modes herein, includingthose of FIG. 3, FIG. 4, FIG. 5, FIG. 6 and FIG. 15 may be applied withthis embodiment.

FIG. 9 shows another embodiment of the channel drive/receive circuitry,which is capable of the same function as the previous two examples butuses four pins labeled 1-4. This embodiment will work on most presentday programmable logic devices but requires two differential digitalinput and two digital output pins plus two resistors and two capacitorsto operate per channel. The digital output drivers at pins 1 and 4 donot require especially high output impedances for this version.Generally, the drive signal generation circuitry 41 is constructed thesame as the previous version, with the control switch 48 being a digitalswitch because the PWM signals from PWM modulators 45 are still digitalentering control switch 48. The sigma-delta D/A converter converting thesensor signal to analog is implemented with a digital output driver 46and a sigma delta output filter made up of output capacitor 47 andresistor R2. This sigma-delta output filter is preferably a single poleRC filter as depicted, with a cutoff frequency of approximately 1 Mhz.This filter output is the analog sensor drive signal 35, which isconnected from the filter output capacitor 47 back into pin 3, to thereference input of comparator 34.

The drive/receive circuit 30 again uses a voltage following sigma-deltaAID converter driven at its reference input with analog sensor signal 35to achieve a sigma-delta analog to digital transceiver. The sigma-deltaDI A portion of the voltage following circuit in this version includesdigital output driver 36 at pin 1, and a sigma delta output filter 38built of external resistor R1 and capacitor C1. The example filter inthis version is a single pole RC filter with a cutoff frequency of about1 Mhz. The various single- and multi-frequency driving and receivingschemes described herein may all be used with this embodiment, includingthe driving process of FIG. 3, FIG. 4, FIG. 5, FIG. 6 and FIG. 15.

FIG. 8B shows another embodiment of a channel driver, which can alsowork on present day programmable logic device designs, requiring onlytwo differential digital input comparator pins and one digital outputpin for a total of three I/O pins per channel used. Its only limitationin this regard is that the mutual capacitive mode transmit channel (themutual signaling is typically used to measure mutually coupledcapacitance but may be used to measure mutual inductance or resistivelycoupled signals), of which there may be only one active at a time,cannot act as a receive for self or pen receive. In the depictedembodiment, the drive signal generation circuitry 41 is common to allthe transmitting drive modules, and is connected to the circuit 30 atseparate locations, the f1 mutual sensor signal being digitallygenerated and fed to be pulse-width modulated in the PWM f1 block 45 inthe upper left of the drawing. This circuitry is internal to the IC.This modulated f1 mutual sensor signal is fed to a digital controlswitch 58, which passes through either the output of the sigma-delta A/Dconverter at node 33, or the PWM f1 signal, to the sigma delta driver36, which is configured as a sigma-delta D/A converter by the connectionto the sigma-delta output filter 38 connected to pin 1. The output offilter 38 is, similarly to the previous figure, connected to virtualsignal node 37, which is connected to the voltage-following sigma-deltaAID converter input on pin 2. Node 37 is also connected to the EMIfilter 39 and, through this filter, coupled to the row electrode to sendand receive the sensor signals similarly to the other versions herein.In this version, as can be seen, the reference input of thevoltage-following sigma-delta A/D converter, at pin 3, is connected tothe analog self-sensor signal. This signal is produced by the otherportion of the drive signal generation circuitry 41, which as showntakes a dithered version of the f2 sensor signal and digitally pulsewidth modulates and drives this signal out an output, where it isfiltered by sigma-delta DI A output filter 47, and then is fed to thecomparator reference node at pin 3. The filter 47 is typically externalto the IC, and the dithered f2 self-sensor signal is driven out a pin tothis filter. This pin is not counted in the pin count of the circuitbecause this single self-sensor signal is used to drive all the otherself-signal transmitting at other drive channels, as shown by the arrowgoing to other drive modules. The mutual sensor signal, in this version,is fed to the other channel drive modules as a digital PWM signal, asseen at circuitry 41 in the upper left of the drawing. The receivedsignal at node 33 is continuously filtered and decimated through to theinternal receiver logic at block 18, similar to the other embodimentsherein. It should be noted that one distinction between the circuit ofFIG. 8B and that of FIG. SA is the difference in the thresholdhysteresis from approximately 30 m V and approximately 150 m V due tothe use of a comparator input in FIG. 8B versus a digital input in FIG.SA. The digital input with a higher hysteresis has more requirements fordither which is shown in FIG. 5A injected in the AID feedback loop atdither block 43.

In operation, it can be understood that the depicted circuit willtypically operate to drive to the sensor electrode and sense from thesensor electrode the f2 self-sensor signal, and simultaneously receivethe f1 signal if it is coupled through from other crossing sensorelectrodes. When in the course of scanning the mutual signal onindividual electrode channels, the drive process reaches this channel,the logic changes switch 58 to feed the f1 mutual signal out, and thedigital signal passed out of the drive module to internal logic is notused during this time.

The signal driving and receiving schemes shown in the diagram of FIG. 3showing self-capacitive and receive signals, the diagram FIG. 4, showingmutual capacitance and self-capacitance without the mutual TX channel,and pen receive mode without the mutual TX channel, and in the diagramof FIG. 5, showing mutual capacitance and pen receive mode without themutual TX channel, may be applied with the embodiment of FIG. 8B.

FIG. 8A shows another embodiment of a channel driver, which is similarin function to the example of FIG. 8B, and is similarly limited in themutual capacitive mode when transmitting. However, this circuit usesonly two digital pins, and so may be better for use in a high channelcount system. The depicted channel driver circuitry 30 may be employedwith in situations where a controllable AC voltage reference isavailable for digital input pins, as seen by the f2 self-sensor signalbeing fed to the voltage reference of the pin 2 receiver, whichfunctions as the sigma-delta comparator in this embodiment. Typically, adigital input pin functions as a comparator but FPGA or PLD designs donot always provide ability to control the reference voltage of suchpins. Where that capability is available, the present circuit may beused, with a common self-signal driven out a pin at PWM and driver45,46, and filtered to create an ADC version of the self-sensor signal35, then fed into a single pin to the driver reference voltage for alldigital input receivers. As shown on the drawing, this scheme is onlypossible if on an FPGA or PLD an AC voltage may be fed to the digitalinput pin references. If not, the scheme must be implemented with acustom ASIC, in which case a 1 pin solution is preferred. Many presentday programmable logic devices exhibit about a 150 m V hysteresis on thedigital input pin, which is considerably greater than the approximately30 m V hysteresis show on the specs for analog comparators in the samehardware. Use of analog comparators is therefore preferred to obtainbetter signal-to-noise ratios, however the depicted circuit may stillenable multi-touch capability with much improved economics over otherprevious sensor driver circuits. The remainder of the circuit functionssimilarly to that of FIG. 8B, and may be used with the same self,mutual, and pen transmit and receive schemes as the circuit of FIG. 8B.

Some alternate embodiments include a solution employing more analogcircuitry, which may be embodied in an ASIC or in circuitry external tothe IC, such as a higher order A/D converter and higher order DIAconverter in the voltage-following sigma-delta converter. Also the useof op-amps configured as voltage follower buffers feeding highresolution analog to digital converters could be used as channeldrivers. These solutions are not ideal due to greatly increased siliconreal estate requirements and associated analog signal handlingrequirements.

Some versions may include a numerically controlled oscillator(s)generating one or more frequencies for drive signals. Such oscillatorsare well understood and common knowledge in the field.

Referring now to the processes of driving and receiving touch sensorsignals, which may be done with circuits described herein or othercircuits, generally various driving and receiving schemes are describedwith respect to FIGS. 2-6 and FIGS. 13-17.

FIG. 2 is a legend for interpreting the signaling diagrams of FIGS. 3-6,13, and 15. At the top, symbols are given for the various analog sensorsignal frequencies f1 (used for mutual coupled signals), f2 (used forself-sensed signals at the same electrode), and f3 (used for a peninjected signal). Next the symbols for transmitting and receiving thevarious signals are shown. The f2 self-signal is shown with a two-wayarrow because it is received or sensed on the same electrode as it istransmitted or driven. The Receive symbol is shown with only an incomingarrow for reception and some small mixed frequency symbol. The f3 penfrequency is shown only as a Receive because it is transmitted from anexternal pen electrode as the pen is moved over and on the touch sensorby a user. The scanning of the mutual transmit symbol, over a series oflines (rows or columns) is shown by the symbol with a wide arrow throughit. Below that, the preferred clock frequency ranges for the embodimentshown in FIG. 1 are listed.

FIG. 3 is a diagram showing an embodiment of a simultaneous drive methodshowing a multi-mode state (Self+Receive), and indicating in the notesthe different pin configurations herein capable of achieving thesignaling scheme. The depicted sensor electrodes in the array are, inthis version, the rows 302 and columns 304 of a touch screen or touchsensor array. As discussed herein, other types of touch sensor array maybe used, and a capacitive multi-touch sensor is preferred. The symbolsindicate that second frequency f2 self-sensor signal is transmitted oneach row 302 and column 304 electrode, and sensed on the sameelectrodes, the sensing is done simultaneously with transmitting, asdescribed above with respect to the drive/receive circuitry.Simultaneously with sending and receiving the second frequency f2self-sensor signal, the third frequency f3 pen sensor signal is receivedor sensed on all rows and columns, transmitted of course from a pen usedwith the touchscreen or touch sensor. While all rows and columns areshown employed in the depicted method, at a minimum not all rows orcolumns have to be used to perform the method. A sub-group may beselected, or a group of all rows and columns.

FIG. 4 is diagram showing an embodiment of a simultaneous drive methodwith a multi-mode state (Self+Receive+Mutual Scan), and indicating innotes the different pin configurations capable of achieving such. Asshown by reference to the symbol legend, the first frequency f1 mutualanalog sensor signal is scanned over successively over each row 302,preferably at a 5 ms total cycle, and received at all the rows 302 andcolumns 304 except the one currently transmitting. When the depictedscan cycle reaches a row, the drive receive circuitry in that rowchanges modes to transmit the f1 mutual sensor signal. This f1 mutualscanning process may, of course, be done with the columns rather thanrows, as their orientation is not important. The scanning process startsagain at the first row when the last row is completed. The secondfrequency f2 self-sensor signal is transmitted and received/sensed onall rows and columns simultaneously except the one currentlytransmitting. Finally, the third frequency f3 pen sensor signal isreceived on all channels simultaneously except the one currentlytransmitting. FIGS. 13 and 14 also describe this signaling scheme. FIG.13 is a diagram showing the resultant signal energies from both humancontact and the pen digitizer which are all sampled in the same 5 mSframe as used in the example timing scheme for FIG. 4. As with the otherdrawings, the particular time period is not limiting and other timeperiods may be used. FIG. 14 is a timing diagram showing a singlecapture frame with simultaneous Self, Pen, and Mutual scan for FIG. 13.As can be seen in FIG. 13, the sensing of the f2 frequency self-signalprovides data stored in a two-dimensional formal, with one dimensionbeing the location from which the data is sensed, along the columns asshown on the bottom, and the other being the signal magnitude of thedata point. More such 2-dimensional data is received from the rows asshown on the Self f2 data set to the right of the array. The size of thebar for each data point represents the signal intensity. The sensedSelff2 data points show touches on the touchscreen as indicated by thefinger touch shown at the large oval on the array. Similarly,2-dimensional data is received for the Pen f3 frequency, with thereceived pen data shown for the columns marked Pen f3 and showing aspike where the pen is depicted placed on the touchscreen. The rows alsoreceive a data spike as seen in the Pen f3 data along the right side ofthe figure, the data spike centered around the depicted pen location. Asdiscussed above, the Pen f3 data represents a signal generated on thepen and coupled into the sensor array, typically capacitively coupled,such that the closest rows and columns to the pen receive a strongersignal while most rows and columns will not detect a signal. Finally, inFIG. 13, the data detected through sensing the f1 mutual analog sensorsignal is provided as a 3-dimensional array, because each detectedsignal magnitude has a row and a column location associated with it,which are the row (or column) for the active mutual TX line when thedata point is detected, and the column (or row) at which the data pointis detected. The third dimension is the magnitude of the signal,providing a three dimensional data array like the Mutual f1 arraydepicted at the bottom of FIG. 13. One benefit of the drive/receivecircuit designs provided herein is that they allow the third frequencyf3 pen data to be received simultaneously using the same circuitryemployed to sense self-data and mutually coupled data. Typically,previous systems either required a separate array to detect pen data orneed to switch the circuitry to a pen mode, not sensing self or mutualdata, to detect the pen, and then switch back to sense touch from one ofself or mutual signals, in a continuous cycle. As shown in the timingdiagram of FIG. 14, the depicted signaling process is shown for a 100row touchscreen or touch sensor over an example cycle period of 5 ms. Asshown in the top row of the timing diagram, all rows and columns mayreceive the self-sensor signal on f2 continuously, except the currentlytransmitting row “current TX row” on which the Mutual TX signal on thefirst frequency f1 is transmitted. The next row of the timing diagramshows that all rows and columns, minus the currently transmitting mutualrow “Mutual TX” again, may receive the pen signal Pen f1. The pen timingdiagram is shown as filling less than all of the time scale depictedbecause the pen signal is not always received, only when a pen is nearor touching the touchscreen or touch sensor.

Still referring to the timing diagram of FIG. 14, the next row labeledMutual TX (f1) shows the mutual signal being transmitted on each row bysequentially scanning it down the rows from row 1 to row 100. Theexample time period on each row is given as 50 uS. The row below showsthat the mutual signal reception (sensing) is done on all columns, toreceive any mutual signal coupled through to any column by touch on thetouch sensor, and the row below that shows the mutual reception is doneon all rows except the row on which the mutual signal is transmitted.While the depicted scheme scans the mutual analog sensor signal over allthe rows, of course the columns could be scanned instead, or both rowsand columns could be scanned in sequence. Further, less than all of therows or columns might be scanned with the mutual signal in anyparticular control scheme. A group may also be selected of less than allof the rows and columns to transmit and sense the self-signal. A methodof driving and receiving signals to and from a multi-touch sensorgenerally includes (a) for each of a first group of electrodescomprising row or column electrodes of the multi-touch sensor,sequentially scanning a mutual analog sensor signal through the group ofelectrodes by feeding it to respective sigma-delta D/A convertersconnected to the respective electrodes, the mutual analog sensor signalcomprising a first frequency; (b) while performing (a), for each of asecond group of electrodes comprising row electrodes or columnelectrodes of the multi-touch sensor, simultaneously driving aself-analog sensor signal through a sigma delta D/A converter onto pinscoupled to the respective row electrodes or column electrodes, therespective self-capacitive analog sensor signals comprising a secondfrequency or a data pattern modulated at a second frequency; (c) foreach of the second group of electrodes used in (b), simultaneouslysampling touch sensor data for at least two different modes of self andmutual, the touch sensor data comprising sensed altered sensor signalsat the first and second frequencies, altered by the impedance of the rowor column electrodes.

FIG. 5 is an embodiment of a simultaneous drive method showing amulti-mode state (Receive+Mutual Scan) and indicating in notes thedifferent pin configurations capable of achieving such. As with theabove versions, the first frequency f1 mutual analog sensor signal isscanned over successively over each row 302, preferably at a 5 ms totalcycle, and received at all the rows 302 and columns 304 except the onecurrently transmitting. When the scan cycle reaches a row, the drivereceive circuitry in that row changes modes to transmit the f1 mutualsensor signal. The rows and columns may, of course, be interchanged. Thescanning process starts again at the first row when the last row iscompleted. The third frequency f3 pen sensor signal is received on allchannels simultaneously with receiving the first frequency f1 sensorsignal, except on the channel currently transmitting. As discussedabove, at a minimum the method is performed by selecting groups of morethan one electrode, which may include all electrodes. The method isgenerally described with the steps of or each of a first group ofelectrodes comprising row or column electrodes of the multi-touchsensor, sequentially scanning a mutual analog sensor signal through thegroup of electrodes by feeding it to respective sigma-delta DIAconverters connected to the respective electrodes, the mutual analogsensor signal comprising a first frequency. While scanning the f1 mutualsensor signal, for each of a second group of electrodes comprising rowelectrodes or column electrodes of the multi-touch sensor, the methodsenses touch sensor mutual data, the touch sensor mutual data comprisingsensed altered sensor signals at the first frequency, altered bycoupling between the row and column electrodes. The method may furtherinclude, simultaneously to the sensing of the mutual data, for each ofthe second group of electrodes, the method simultaneously samples a penanalog sensor signal transmitted from a pen at a frequency differentfrom the first frequency using the same A/D converter performing themutual sensing. The simultaneous sampling may be performed by a voltagefollowing sigma delta A/D converter integrated with each sigma-delta DIAconverter driving the respective row or column electrodes, the voltagefollowing A/D converter having a comparator with a first referencecomparator input and a second comparator input, the second comparatorinput connected to the sigma-delta D/A converter output. Generally, thecircuit of FIG. 7 may be used or any of the circuit embodimentsidentified in FIG. 5, or other suitable circuits may be used. Theself-transmit signal not necessarily active in this particular method.

FIG. 6 is a diagram of an embodiment of a simultaneous drive methodshowing a multi-mode state (Self+Receive+Mutual Scan) and indicating thedifferent pin configurations capable of achieving such. FIG. 6 showsfull signal function with all modes of mutual and self, and receiveactive. As shown by the symbols and their legend, the first frequency f1mutual analog sensor signal is scanned over successively over each row302, preferably at a 5 ms total cycle, and received at all the rows 302and columns 304 including the one currently transmitting the mutualsignal. This f1 mutual scanning process may, of course, be done with thecolumns rather than rows, as their orientation is not important. Thescanning process starts again at the first row when the last row iscompleted. The second frequency f2 self-sensor signal is transmitted andreceived/sensed on all rows and columns simultaneously. Finally, thethird frequency f3 pen sensor signal is received on all channelssimultaneously. As discussed with respect to the other methods, groupsof less than all rows or less than all columns may be employed withoutdeparting from the general methods described herein. For example, if aparticular device were to not sense on particular rows or columns, butgenerally perform the methods herein, it would use the groups ofelectrodes as described herein. FIGS. 13 and 14 also describe thissignaling scheme, except that for this process, the labels on the topright of FIG. 14 of Selff2 RX/TX (All Col+Row) should not exclude thecurrently transmitting row as done with regard to FIG. 4, because thecircuit arrangements listed (4. Pin minimum function, 2 Pin Special, and1 Pin Special of FIGS. 9-11) allow control of the circuit modes toreceive the self f2 and pen f3 signals on all rows, even that currentlytransmitting the mutual signal. It is understood for all of theseschemes that the rows and columns may be switched, and non-traditionallyshaped arrays may also be employed with the circuitry and schemesdescribed herein.

FIG. 15 is diagram showing an embodiment of a simultaneous drive methodshowing a multi-mode state (Self+Receive+Dual Mutual Scan) andindicating the different pin configurations capable of achieving such.The depicted method employs a dual axis scan scheme where operationduring independent mutual capacitive mode or simultaneously with othersampling and driving modes can be achieved. The scan uses an additionalfourth frequency for an independent mutual scan that is conductedsimultaneously to the f1 mutual scan. For example, TX (transmit f1) onrows 302 and RX (receive f1) on Columns 304. TX mutual frequency f4 onColumns 304 and RX mutual frequency f4 on Rows 302. While theseindependent mutual scans proceed, the self-analog sensor signal atfrequency f2 is transmitted and sensed on all the rows and columns, andthe pen signal is sensed on all rows and columns. It is understood thatthe same drive/receive circuitry is configured in its different modes toperform the mutual scan as it cycles through each particular row.Generally, the method can proceed with less than all rows or columns insome situations, and includes for each of a first group of electrodescomprising row or column electrodes of the multi-touch sensor,sequentially scanning a mutual analog sensor signal through the group ofelectrodes by feeding it to respective sigma-delta DIA convertersconnected to the respective electrodes, the mutual analog sensor signalcomprising a first frequency. While doing so, the method for each of asecond group of electrodes comprising row electrodes or columnelectrodes of the multi-touch sensor, simultaneously drives aself-analog sensor signal through a sigma-delta D/A converter onto pinscoupled to the respective row electrodes or column electrodes, therespective self-analog sensor signals comprising a second frequency or adata pattern modulated at a second frequency. For each of the secondgroup of electrodes, the method simultaneously sampling touch sensordata for at least two different modes of self and mutual, the touchsensor data comprising sensed altered sensor signals at the first andsecond frequencies, altered by the impedance of the row or columnelectrodes. For each of the first group of electrodes and the secondgroup of electrodes, the method simultaneously samples a third penanalog sensor signal a third transmitted from a pen at a third frequencydifferent from the first and second frequencies. To accomplish the dualmutual scan, the method performs for each of the rows or columns thatare not driven with the mutual analog sensor signal f1 (in this diagram,the columns), scanning a second mutual analog sensor signal sequentiallythrough respective sigma-delta DIA converters onto pins coupled to therespective row or column electrodes, the second mutual analog sensorsignal at a fourth frequency different from the first and secondfrequencies and different from a third pen frequency if a pen frequencyis employed in the method. Then for each of the for each of the rows orcolumns that are driven with the f1 mutual signal, the methodsimultaneously samples touch sensor data for at least two differentmodes of self and mutual, the touch sensor data comprising receivedaltered sensor signals at the second and fourth frequencies. The methodmay accomplish the simultaneous sampling using a voltage following sigmadelta A/D converter integrated with each sigma-delta D/A converterdriving the respective row or column electrodes, the voltage followingA/D converter having a comparator with a first reference comparatorinput and a second comparator input, the first reference comparatorinput receiving the self-analog sensor signal and the second comparatorinput connected to the sigma-delta D/A converter output. The two mutualsignals may be added when the mutual mode is activated in the cycle byswitching or coupling in the mutual signals in the manner shown in thevarious drive/receive circuit diagrams. The f4 mutual signal isgenerated digitally and may be fed to multiple channel drivers similarlyto the f1 mutual signal as described in the various embodiments.

FIG. 12 is a block diagram showing an embodiment of a CICFilter/Decimation/Demodulation/Amp/Phase sample chain showing resolutionof three different simultaneous frequencies representing three separatemodes of touchscreen function according to some embodiments. Thereceived signal from the comparator output is passed to filter anddecimation block, which in this version is implemented with CIC(cascaded integrator-comb) filtering, at least at the initial filteringstages. At block 1202, the filtering process starts with a CICintegrator, followed at block 1204 with a decimator reducing the samplerate to 1 to 4 Mhz. Next at block 1206, a CIC decimator is provided ifnecessary to remove DC components of the signal. At block 1208, acompensation FIR is provided if necessary to compensate for the effectsof prior CIC filtering, such as passband droop and wide transitionregion.

The resulting data is sent to blocks 1210 where the signals areQuadrature Baseband Demodulated and the generated FQ data is sent toblocks 1212 where Amplitude, Phase, and Magnitude are calculated and maybe further filtered and decimated before being sent to Memory 1214 forstorage and further DSP processing if necessary. The changes to theAmplitude, Phase, and Magnitude over time for each signal are then usedto determine the presence of objects interacting with the sensors suchas fingers or pens. Typically, the Self (f2) signals change by verysmall phase shifts, and Mutual (f1) and Pen (f1), received signals,change in amplitude. While quadrature baseband demodulation is describedhere, this is not limiting and many other suitable demodulation schemesmay be used to extract the sensed signals in a form usable by the systemto interpret touch.

FIG. 16 is a diagram showing prior art self-capacitance measurement withshielding elements and the current invention with all elementssimultaneously driven. One significant advantage of the circuits hereinmay be observed on the figure, in that the noise caused by a conductivecontaminant present on the touch sensor is greatly reduced when all rowsand columns in the sensor array are driven as the circuits and methodsherein enable.

Referring back to the system block diagram of FIG. 1, the systemincludes several functional blocks that one of ordinary skill in the artcan implement after appreciating this specification and the constructiondirections below.

Dither Generator:

Some embodiments of the invention use the same dither on all channels asa method of achieving very similar sampling of system and external noiseor alternately introducing a simple delay for each channel to allow forcontrolled same dither or semi-random dither generation.

A single dither signal generator may be used to supply a dither signalall the driver channels of the device. In some cases and modes, it maybe beneficial to set all the dither signals to the same instant value soas to improve simultaneous sampling external noise recognition but insome cases having semi-random dither between channels could provebeneficial. Where the dither mixing occurs in the channel driver (anon-common dither source), a simple register delay scheme of only fourpositions allows enough differentiation from channel to channel.

Some embodiments of the invention provide improved resolution via use ofshaped dither in combination with the continuous low frequency and lowamplitude self-capacitive signal used as a reference to overcomehysteresis and quantization on the self-capacitance mode signals as wellas other signals of interest such as the mutual capacitance receive andor pen receive signals.

In the Sigma Delta Analog to Digital Converter, dither noise is used toimprove resolution and to overcome inherent hysteresis in the digital1-bit ADC input or comparator. In current hardware this could be as lowas 30 m V and or as high as 200 m V. Without dither the hysteresis willcause reduced resolution due to quantization caused by the DAC portionof the SD ADC having to charge the RC filter beyond the value requiredto match the reference voltage to the point where the hysteresisthreshold is overcome-this process must then have to be reversed and theRC voltage must be discharged to pass the lower hysteresis bound. Thiscreates a stair stepped “quantized” response.

Adding dither is a way of introducing a known noise to the system thatis easily removed by subsequent filtering. Dithering effectively movesthe signal randomly closer to the upper or lower hysteresis threshold sothe true signal can trip the upper and lower threshold in a more averageway. Using a continuously changing analog signal to allow frequency andlow amplitude also achieves this effect to some extent. By using ditherin combination with a continuous frequency of low amplitude (ex. 30 m Vto 300 m V) even large hysteresis can be overcome for other lowamplitude signals of interest while allowing for all-self-measurement atthe continuous frequency.

Advanced Modulation Schemes:

Some embodiments of the invention use well known modulation schemes,such as PSK, but directed in a novel way towards removing coherentinterfering signals at the same frequency as the driving frequency. Forexample, FIG. 17 depicts a PSK coherent synchronous demodulation: Asingle frequency signal may be generated with a numerically controlledoscillator (NCO) and passed through a 50% duty cycle 180 deg phase shiftmodulation. This signal is dithered and then driven to touch sensorelectrode as a self-analog sensor signal according to the techniquesherein. The recovered, or sensed, self-signal is be filtered anddecimated, and demodulated against the 50% duty cycle 180 deg phasemodulation to produce a baseband continuous non-phase modulated signal.The single frequency is recovered with the benefit of now having anycoherent interfering signal at the same frequency reduced or highlyrejected.

As another example, an FSK coherent synchronous demodulation scheme maybe used instead: A dual frequency signal may be generated with a 50%duty cycle. The recovered signal can be filtered and decimated anddemodulated against the 50% duty cycle to produce a baseband continuoussingle frequency (DC) signal; the single frequency is recovered with thebenefit of now having any coherent interfering signal at the samefrequency reduced or highly rejected.

CIC Decimator:

In an example version of the CIC decimator filter, the signal from thechannel driver is converted from a 1-bit high frequency signal to a muchlower frequency high resolution signal, filtered, and decimated with theCIC filter (example capability and speed as shown in FIG. 18).Decimation down ratio range of 400:1 to 100:1 will develop a finalsignal of 1 to 4 MHz and resolution of 14 to 16 bits per sample. Thesevalues can be adjusted to improve resolution, sample speed, and powerconsumption. The decimated channel signal contains the different modesignals (self-capacitance signal, for example at 200 KHz, Mutualcapacitance signal, for example at 100 KHz, pen receive signal, forexample at 150 KHz, and also unwanted noise signals) and these signalshave to be broken out into their respective paths and further processed.

Phase and Amplitude Detector:

While many well-known methods exist for determining the phase andamplitude of a signal and picking a specific signal out of a grouping ofsignals (IQ demodulation being the most technical), for the purpose ofthis description and for simplicity the Goertzel method suffices toresolve the phase and amplitude of for each signal on a frame by framebasis. In various implementations, the Goertzel method can be modifiedto handle the advanced noise reduction modulation scheme described abovebut may be limited where for example an electrostatic pen is sendingdigital information using FSK, PSK, amplitude, or phase modulation, ortiming between signals is concerned. Capturing this digital data willrequire a more advanced scheme on the pen signal path. These schemes arewell understood in the industry.

Sequencing Generator:

To allow for different configurations of touchscreens to be driven andthe resulting data to be mapped into memory in a known and controlledmanor, a method of configuration is required that allows any driverchannel to be placed into any drive order and also the resultant data tobe mapped into a known area of memory such that the procedures requiredfor the higher level blob (large noisy touchscreen contact) tracking canaccess the memory in an optimized and systematic way that does notrequire the customization of code or drivers for different size andshape sensors. This typically requires configuration arrays, adefinition of how the resultant data will be mapped in memory, anddefinition of how and when the sensor array will be driven.

Configurable Memory Mapped Area:

The Memory Array block includes memory to store configuration arrays,resultant 2D and 3D signal levels arrays, buffer arrays, filter resultarrays, and calibration arrays.

Filter Module:

To automate the repetitive tasks such as base line calibrationsubtraction, normalization, and filtering, the filter module worksduring frame data receipt and or between frames to process the receiveddata. Processing the columns data just after completion of the row drivein the case of mutual capacitive is ideal as long as the filterprocessing does not interfere with the memory access of the next line ofreceived data. Advanced memory access schemes can be used to preventsimultaneous access problems or a buffer scheme can be used to alterdata in one buffer while the next buffer frame is filled.

Processor System:

Well understood and common knowledge in the field. As depicted in FIG.1, any suitable processor core for an ASIC or FPGA may be used invarious implementations.

Filter Methods:

The novel methods of noise removal herein using the simultaneous sampleddata including noise, are directed towards removing coherent or spuriousinterfering noise signals in the touch data through the identificationand removal of the noise which appears as common mode proportionalchanges in the sampled data.

Subtraction of common mode proportional noise in the touch data on apCap (Projected Capacitive) sensor is a technique only possible due tothe simultaneous sampling characteristics of the present invention. Auser touching the system can act as an antenna and inject noise into thesystem. Alternately, the user may effectively act as drain to a commonmode noise on the system. It is impossible to tell the differencebecause the noise is only seen at the touch location and the noise isproportional to the touch energy. A hard touch typically causes thehighest capacitive coupling at the center of the touch due to thecurvature of a finger and the pressure applied. The finger can bethought of as a low impedance source or sink for the noise. A touchmeasurement at the side of the finger may have half the touch energy asa touch measurement in the center due to capacitor plate area anddistance. The noise on the center reading may have a SNR of 10 and theside reading will also have a SNR of 10.

If the touch readings are randomized or split in time or demodulationmethod, there will be no possibility of knowing the touch energy tonoise energy at any instant of time, only the average noise over time.The self-capacitive signal mode of the present invention samples all therows and columns at the same time using the same modulation scheme andfiltering so all of the rows and columns will show an impulse of noiseas a plus or minus to the touch profile energy. The mutual capacitancesignal mode is a line scan (row) mode with simultaneous alternate line(columns) receive so all of the alternate lines (columns) will show animpulse of noise as a plus or minus to the touch profile energy underthe driven line (row). Using both self and mutual data the noise changefrom frame to frame can be identified and directly reduced via linear ornon-linear techniques.

FIG. 19 is a simple simulated example of the drive channel signalsshowing the drive, dither, and following (sensed) signals. Depicted arethe self-drive signal 1902, the mutual drive signal 1904, a LowFrequency Dither signal 1906, the sum of these signals that is driven tothe reference following node of the driver, the virtual signal node,S+M+D 1908, and the resultant sigma-delta following signal 1910 whichrepresents the drive/receive circuit's sampled sensor signal as is it isdriven by the sigma-delta following circuit onto the sensor electrode.

CONCLUSION, RAMIFICATIONS AND SCOPE

The driver channel circuitry according to some embodiments of thepresent invention provides an apparatus and method for enhancing thedevelopment, performance, flexibility, and immunity of the multi-touchsystem.

While some embodiments of the invention are shown and described, it isto be distinctly understood that this invention is not limited theretobut may be variously embodied. From the foregoing description, it willbe apparent that various changes may be made without departing from thespirit and scope of the invention as defined by the claims. Accordingly,the scope of the invention should not be determined not by theembodiments illustrated.

Multiple individual inventions are described herein. The inventions arepatentable separately and in combinations. The combinations of featuresdescribed herein should not be interpreted to be limiting, and thefeatures herein may be used in any working combination orsub-combination according to the invention. This description shouldtherefore be interpreted as providing written support for any workingcombination or sub-combination of the features herein. Various signalingand signal processing functions described above can be implemented ineither hardware or software.

As one of ordinary skill in the art will readily appreciate from thedisclosure of the present invention, processes, machines, manufacture,compositions of matter, means, methods, or steps, presently existing orlater to be developed that perform substantially the same function orachieve substantially the same result as the corresponding embodimentsdescribed herein may be utilized according to the present invention.Accordingly, the appended claims are intended to include within theirscope such processes, machines, manufacture, compositions of matter,means, methods, or steps.

What is claimed is:
 1. A touch sensor circuit comprises: a plurality ofdrive/receive circuits for driving and receiving signals from amulti-touch sensor, wherein a drive/receive circuit of the plurality ofdrive/receive circuits includes: an analog to digital conversion circuithaving a first input, a second input, and an output, wherein: the firstinput is coupled to receive a sensor signal on an electrode of themulti-touch sensor, wherein the sensor signal includes a drive signalcomponent and a receive signal component; the second input is coupled toreceive an analog reference signal that includes at least one signalcomponent; and the analog to digital conversion circuit generates adigital signal based on the analog reference signal and the sensorsignal, wherein the digital signal is outputted via the output; and adigital to analog conversion circuit coupled to convert the digitalsignal into the drive signal component, wherein the receive signalcomponent is representative of an impedance on the electrode detectedwhile the drive signal component is applied to the electrode, andwherein detection of an impedance change of the impedance of theelectrode is indicative of a touch proximal to the electrode; and adrive signal generation circuit operable to generate the analogreference signal.
 2. The touch sensor circuit of claim 1, wherein theanalog reference signal comprises: a self-reference signal forfacilitating detection of the impedance change of a self-touch proximalto the electrode; and a mutual-reference signal for facilitatingdetection of the impedance change of a mutual-touch proximal to theelectrode.
 3. The touch sensor circuit of claim 1, wherein the analog todigital conversion circuit comprises: a sigma-delta comparator operableto: receive the sensor signal and the analog reference signal; andgenerate the digital signal based on the analog reference signal and thesensor signal.
 4. The touch sensor circuit of claim 1, wherein theanalog to digital conversion circuit comprises: a sigma-delta comparatoroperable to: receive the sensor signal and the analog reference signal;and generate a first digital signal based on the analog reference signaland the sensor signal, wherein the first digital signal is at a firstfrequency rate; and a flip-flop operable to convert the first digitalsignal into the digital signal by adjusting the first frequency rate toa desired frequency rate.
 5. The touch sensor circuit of claim 1,wherein the analog to digital conversion circuit comprises: a comparatorwith hysteresis, wherein the comparator is operable to: receive thesensor signal and the analog reference signal; and generate the digitalsignal based on the analog reference signal and the sensor signal. 6.The touch sensor circuit of claim 1, wherein the digital to analogconversion circuit comprises: a sigma-delta driver operable to convertthe digital signal into the drive signal component.
 7. The touch sensorcircuit of claim 1, wherein the digital to analog conversion circuitcomprises: a sigma-delta driver operable to convert the digital signalinto an analog drive signal; and an output filter operable to low passfilter the analog drive signal to produce the drive signal component. 8.The touch sensor circuit of claim 1 further comprises: a low pass filteroperable to filter the digital signal to produce a filtered digitalsignal; and a decimator operable to reduce sample rate of the filtereddigital signal to produce a digital representation of the impedancechange of the impedance of the electrode.
 9. A drive/receive circuit fordriving and receiving signals on a single node, wherein thedrive/receive circuit comprises: an analog to digital conversion circuithaving a first input, a second input, and an output, wherein: the firstinput is coupled to receive a sensor signal on a node, wherein thesensor signal includes a drive signal component and a receive signalcomponent; the second input is coupled to receive an analog referencesignal that includes at least one signal component; and the analog todigital conversion circuit generates a digital signal based on theanalog reference signal and the sensor signal, wherein the digitalsignal is outputted via the output; and a digital to analog conversioncircuit coupled to convert the digital signal into the drive signalcomponent, wherein the receive signal component is representative of animpedance of a circuit coupled to the node detected while the drivesignal component is applied to the node, and wherein detection ofchanges in the receive signal correspond to changes in the impedance ofthe circuit.
 10. The drive/receive circuit of claim 9, wherein theanalog reference signal comprises: a self-reference signal forfacilitating detection of the impedance change of a self-touch proximalto the electrode; and a mutual-reference signal for facilitatingdetection of the impedance change of a mutual-touch proximal to theelectrode.
 11. The drive/receive circuit of claim 9, wherein the analogto digital conversion circuit comprises: a sigma-delta comparatoroperable to: receive the sensor signal and the analog reference signal;and generate the digital signal based on the analog reference signal andthe sensor signal.
 12. The drive/receive circuit of claim 9, wherein theanalog to digital conversion circuit comprises: a sigma-delta comparatoroperable to: receive the sensor signal and the analog reference signal;and generate a first digital signal based on the analog reference signaland the sensor signal, wherein the first digital signal is at a firstfrequency rate; and a flip-flop operable to convert the first digitalsignal into the digital signal by adjusting the first frequency rate toa desired frequency rate.
 13. The drive/receive circuit of claim 9,wherein the analog to digital conversion circuit comprises: a comparatorwith hysteresis, wherein the comparator is operable to: receive thesensor signal and the analog reference signal; and generate the digitalsignal based on the analog reference signal and the sensor signal. 14.The drive/receive circuit of claim 9, wherein the digital to analogconversion circuit comprises: a sigma-delta driver operable to convertthe digital signal into the drive signal component.
 15. Thedrive/receive circuit of claim 9, wherein the digital to analogconversion circuit comprises: a sigma-delta driver operable to convertthe digital signal into an analog drive signal; and an output filteroperable to low pass filter the analog drive signal to produce the drivesignal component.
 16. The drive/receive circuit of claim 9 furthercomprises: a low pass filter operable to filter the digital signal toproduce a filtered digital signal; and a decimator operable to reducesample rate of the filtered digital signal to produce a digitalrepresentation of the impedance change of the impedance of theelectrode.